1. Field of the Invention
The invention relates to a piston/cylinder unit having a closed cylinder, a piston guided in an axially displaceable manner in the cylinder and sealed with respect to the cylinder by an annular seal which radially surrounds the piston, the piston dividing the cylinder interior into first and a second working spaces which are filled with a fluid, a piston rod connected to the piston and extending through the cylinder interior, an end side of the piston rod being sealingly guided to the outside of the cylinder through at least one closing wall of the cylinder, a first nonreturn valve with a closing element force-loaded in the closing direction and which can be opened connecting the first working space to the second working space under a high pressure in the first working space, and a second nonreturn valve having a closing element force-loaded in the closing direction and which can be opened connecting the second working space to the first working space under a high pressure in the second working space.
2. Description of the Related Art
Piston/cylinder units of the type described above are used, for example, as infinitely variable door arresters for motor vehicle doors. When used in this application, the two nonreturn valves are closed when the door is not being moved such that the door is held in the position which it has assumed at that particular instance. If the door is actuated manually to move it out of this position, a pressure is built up in one of the working chambers, the high pressure causing a non-return valve associated with that working chamber to open. Once the valve opens, fluid is allowed to flow out of the working chamber with high pressure into the other working chamber.
To open the valve, a pressure which overcomes the force loading of the closing element in the closing direction has to be built up in the working chamber. If the force of the manual actuation of the door is reduced below a certain extent before the door has been moved to its desired position, the pressure in the working chamber is reduced such that the nonreturn valve also closes and the movement of the door is blocked by the piston/cylinder unit even if a further movement of the door is still desired.